1. Field of the Invention
The present invention concerns an alarm or warning system for predictive maintenance, in a constant temperature liquid circulating apparatus which supplies a constant temperature cooling liquid to a load in accordance with operation of a three-way proportional valve.
2. Description of the Related Art
In various kinds of mechanical devices having constant temperature components, for example in the case of a semiconductor processing apparatus, a constant temperature cooling liquid (typically a brine solution) is continuously supplied to the constant temperature component (load) of the apparatus, wherein it is necessary to maintain a fixed temperature at the load. For this purpose, a constant temperature liquid circulating apparatus (also known as a xe2x80x9cchillerxe2x80x9d unit) is provided for supplying a constant temperature cooling liquid, wherein the cooling liquid which has risen in temperature by the load is circulated back to the constant temperature liquid circulating apparatus and, after being chilled by contact with a refrigerant in a heat exchanger, heat is then applied to the cooling liquid from a heater to establish a fixed temperature for the cooling liquid, and the cooling liquid is resupplied to the load in a circulatory manner.
The constant temperature liquid circulating apparatus, as understood from the description above, is not only for connection to a semiconductor processing apparatus, but may also be connected to other mechanical or electrical devices (master devices) in various industrial areas for which temperature control is required for supporting their proper operation. Therefore, breakdown or irregular operation of the constant temperature liquid circulating apparatus is directly related to stoppage of the master apparatus to which it is attached, with the possibility of creating large scale failure and loss.
More specifically, the constant temperature liquid circulating apparatus generally comprises a refrigeration circuit for cooling, in a heat exchanger, the cooling liquid that is returned from the load, and a cooling liquid circulating circuit for adjusting to a fixed temperature by applied heating the cooling liquid which has been chilled in the heat exchanger, and discharging the same, as well as other operating equipment therefor. The structural elements making up the aforementioned refrigeration circuit and cooling liquid circulating circuit, and the operating equipment therefor, are made up of a large number of parts. Even if one of the structural parts develops a fault, there is not only the possibility for breakdown or irregular operation of the constant temperature liquid circulating apparatus itself, but irregular operation or operational stoppage of the master device attached thereto may also occur, and in extreme cases, may cause a complete breakdown of the master device itself.
Accordingly, it is necessary to consider how to avoid irregular conditions in such a constant temperature liquid circulating apparatus, while at the same time is it very important to take preventative safety measures before such irregular conditions arise. However, when the constant temperature liquid circulating apparatus is used, there is a tendency, from the standpoint of rising costs, not to continuously perform careful observation thereof. Moreover, even when observations of the apparatus are regularly made, it is not possible to avoid natural wear and tear of parts which occur with the passage of time, and as a result, the useful life of the parts, and natural breakdown thereof, cannot be avoided. Thus, so called post-event processing, that is, methods for investigating the cause only after an irregular condition has occurred in the constant temperature liquid circulating apparatus, with exchange of parts and the like, have been required. With such methods, however, the time for restoration of the apparatus is lengthened, and large scale losses can occur.
As one system which attempts to deal with this type of problem, a so called xe2x80x9cremote maintenancexe2x80x9d system is known. This system is one in which the running state of an apparatus is observed using various kinds of sensors, and when a breakdown or irregular condition occurs, information about the state of the apparatus is transmitted to a predetermined location using telephone lines, so that service personnel can be quickly dispatched for conducting repairs. Notwithstanding, this system also involves post-event processing in which repair work is not begun until after the constant temperature liquid circulating apparatus develops a breakdown or irregular condition, wherein required repairs can be hastened only to a certain extent.
In order to address some of the problems indicated above, one approach has been proposed as described in Japanese Laid-Open Patent Publication No. 11-37516. This system attempts to minimize apparatus downtime by inferring the parts which require maintenance, and time intervals at which maintenance therefor is needed, in a constant temperature liquid circulating apparatus before the occurrence of an irregular condition.
As shown in FIG. 5, such a constant temperature liquid circulating apparatus is made up of a refrigeration circuit and a cooling liquid circulating circuit. The refrigeration circuit comprises a compressor 61, a condenser 62, a pressure-reducing valve 63, an evaporator 64 and an accumulator 65, all of which are connected in series. The refrigeration circuit section also includes an overheat prevention circuit 66 that directly returns the compressed refrigerant to an accumulator 65 when the evaporator 64 is subjected to a large load, including an overheat prevention valve 66a in the circuit 66 that opens and closes the overheat prevention circuit 66 based on readings from a temperature sensor 66b located on the upstream side of the accumulator 65 for detecting the temperature of the refrigerant.
On the other hand, the cooling liquid circulating circuit comprises a heat exchanger 71, in which heat exchange occurs between the refrigerant and the cooling liquid that is circulated back after having risen in temperature by the load, a cooling liquid tank 72 having a heater 73 installed therein, and a pump 74 which supplies and circulates the cooling liquid to the load which has been heated to a fixed temperature by the heater 73, all of which are interconnected in series.
As a result, the cooling liquid which has risen in temperature by the load is chilled by the refrigerant of the refrigeration circuit which flows through the evaporator 64 arranged in the heat exchanger 71.
In addition, a temperature sensor 75 that detects the temperature of the cooling liquid and outputs a signal thereof is provided near an outlet of the tank 72, and a temperature controller 76 is installed in the circulating circuit section to control the amount of power supplied to the heater 73 based on the output signal from the temperature sensor 75. The temperature controller 76 compares the temperature detected by the temperature sensor 75 with a set temperature for the cooling liquid in order to control the amount of power supplied to the heater 73, i.e., the amount of heat provided in the tank 72.
Such a constant temperature liquid circulating apparatus includes a predictive maintenance system which comprises additional sensors for continuously monitoring various condition amounts, the sensors being provided at respective components of the apparatus. From the condition amounts of the apparatus which are obtained as outputs of the sensors, internal components and parts requiring maintenance, and maintenance time intervals therefor, are inferred. Further, a warning means 81 is also provided for issuing a warning when a warning condition exists, but before a serious irregular condition or breakdown actually takes place.
More specifically, in this predictive maintenance system, as sensors for continuously monitoring various types of conditions, sensors for detecting changes in condition amounts including the temperatures of various components, electrical current amounts for electrically operated driving parts, refrigerant pressure, cooling liquid flow amounts, and the like, may be set up in the constant temperature liquid circulating apparatus. Further, the warning means 81 is provided for inferring which parts require maintenance, along with maintenance time intervals therefor, and for issuing a warning from changes in condition amounts of the various internal parts of the apparatus that are obtained as outputs from the sensors. Or, as the aforementioned sensors, sensing means may be provided within the constant temperature liquid circulating apparatus for detecting accumulated amounts of the number of ON/OFF times of mechanical parts including valves, and/or current supply time intervals to the heater, wherein a warning means is provided for inferring the parts which require maintenance and maintenance time intervals therefor, and for issuing a warning from changes in the condition amounts of the various internal parts of the apparatus that are obtained as outputs from such sensors.
Thus, unlike post-event processing that takes place only after detection of a breakdown or irregular condition, a warning can be issued from the warning means 81 before occurrence of a breakdown or irregular condition, so that timely maintenance thereof can be urged. The warning is not only provided on an operational display part of the constant temperature liquid circulating apparatus itself, but in addition may be applied to an operational display part of a master device or in a control room. Further, Laid-Open Publication No. 11-37516 indicates that warning indications may be transmitted to a remote location via telephone lines. As a result, parts requiring maintenance and maintenance time intervals therefor are inferred prior to the occurrence of an irregular condition, so that the downtime of the apparatus can be minimized.
An example of operation of the aforementioned known predictive maintenance system is shown in FIGS. 6(A) and 6(B). A time-wise variation of the cooling capacity is detected based on the temperature data obtained from the temperature sensor 75 disposed in a cooling liquid circulating tank 72, and an irregular operational condition is judged from such a variation. First, in the constant temperature liquid circulating apparatus, the cooling capacity data (output from the cooling liquid temperature sensor 75) possesses a normal characteristic as shown typically in FIG. 6(A). When a fault or irregular condition is beginning to appear, such a characteristic tends to change as shown in FIG. 6(B). More specifically, a change in the characteristic occurs wherein the temperature variation period of the cooling liquid (i.e., the length of time it takes for the temperature to change,) expands from T1 to T2.
When the temperature data is obtained as shown in FIGS. 6(A) and 6(B), in an arithmetic control unit which makes up the warning means 81, a judgement is made and an alarm or warning is issued, whereby the need for maintenance of the constant temperature liquid circulating apparatus can be pre-estimated. Further, in the case that the data detected by other sensors deviates from their proper value ranges, exceeding an upper or lower limit at which an irregular condition is possible, or in the case of deviation from a judgement standard for judging irregular operation, or further in the case that the number or ON/OFF times of mechanical operating parts exceeds an operational limit, or if the usage time of the heater or other expendable parts exceeds a limit value, a warning may be issued according to a similar sort of judgement.
However, in the apparatus shown in FIG. 5, in order to control the temperature of the cooling liquid in the tank 72, after chilling of the cooling liquid through contact with the evaporator 64 in the heat exchanger 71, heat is then applied to the cooling liquid. That is, after cooling in excess of a predetermined temperature, it is necessary to apply heat to the cooling liquid using the heater 73. Thus, chilling of the cooling liquid and subsequent heating are handled using separate operations which tends to result in wasting of energy.
In order to address such a problem, according to Japanese Utility Model Disclosure Document No. 5-17535, a temperature control apparatus has been proposed in which it is possible to control temperature over a wider temperature range with higher precision, and moreover, in which energy consumption is lower. Such an apparatus, as shown in FIG. 7, is characterized by a refrigeration circuit and cooling liquid circulating circuit similar to that shown in FIG. 5, but wherein the cooling liquid circulating passage further comprises an auxiliary coolant path 78 which branches from an outlet side of the pump 74, and then passes through an ON/OFF type of electromagnetic valve 79 and the heat-exchanger 61, providing fluid transport in a recirculating manner back to the tank 62. Further, the temperature controller 76 causes the ON/OFF type electromagnetic valve 79 to open when the temperature of the cooling liquid in the tank 72 is higher than a preset temperature, and causes electricity to be supplied to the heater 73 when the cooling liquid temperature falls below a preset temperature.
The basic operation of the this known type of apparatus may be described as follows. In a case in which the temperature of the cooling liquid in the tank 72 is higher than a preset temperature, the ON/OFF electromagnetic valve 79 is opened by the temperature controller 76, so that the cooling liquid which flows through the auxiliary coolant flow path 78 is chilled by the heat exchanger and quickly recirculates back to the tank 72. In the case that the cooling liquid temperature becomes lower than a preset temperature set in the temperature controller 76, the ON/OFF electromagnetic valve 79 is closed together with applying heat from the heater 73, so that the temperature of the cooling liquid in the tank 72 can be maintained inside the preset temperature range of the temperature controller 76.
Because cooling of the cooling liquid in the auxiliary coolant path 78, as well as application of heat by the heater 73, is selectively performed by raising and lowering the cooling liquid temperature with respect to the preset temperature range, compared to the case of applying heat by a heater to a previously-cooled cooling liquid for controlling to a set temperature range, consumption of energy can be lessened overall, while notwithstanding, the temperature control is highly accurate. Further, by selectively cooling and applying heat to the cooling liquid, control over a wider temperature range is made possible.
However, the apparatus according to Japanese Utility Model Disclosure Document No. 5-17535 has experienced problems of its own. In particular, this apparatus uses an electromagnetic ON/OFF type valve 79 and a heater 73, making up an ON/OFF system, which enables temperature control over a wide range from about xe2x88x9220xc2x0 C. to +90xc2x0 C. However, because of use of the ON/OFF type of electromagnetic valve 79, during abrupt ON/OFF switching operations of the electromagnetic valve, an undesirable xe2x80x9cwater hammerxe2x80x9d effect has been generated. The problem is all the more aggravated in the case of large capacity chiller units, resulting in a cumbersome and vexing disadvantage which has yet to be fully solved. Because of the water hammer effect, it has not been possible to implement this system in large capacity chiller units.
An object of the present invention is to overcome the problems of the water hammer effect and to enable operation of a predictive maintenance system in larger capacity chiller units.
To accomplish this aim, and in order to determine parts and locations requiring maintenance work and maintenance time intervals before the occurrence of an irregular operation, so that any downtime in operation of the constant temperature liquid circulating apparatus is made as short as possible, a system according to the present invention is provided in which respective components of the apparatus are provided with sensors for use in monitoring various kinds of condition amounts in a continuous manner. Especially, among such components, a three-way proportional valve is provided between the outlet of a heat exchanger and inlet to a holding tank, in a cooling liquid circulating circuit which supplies a constant temperature cooling liquid to a load, and a sensor is provided which detects a degree of opening of the three-way proportional valve. A trend line of the three-way proportional valve opening is monitored continuously, and when the trend line shows signs of rising above a certain valve opening degree, such a tend is taken as an indication that the cooling capacity of the apparatus may be decreasing, and preventative measures are undertaken to investigate the cause of such irregular operation.